I have a pair of '99 optimax saltwaters. One motor has low water pressure that I cannot correct. Both a mechancial gauge connected to the compressor water jacket and the DDT confirm the low pressure. I have replaced the water pump, checked the top screen (top of block), checked the check valve, thermostats and still no improvement. last week I switched the lower units which confirmed the issue is not the water pump. This engine has had this problem off and on for about 3 years and appears to actually completely clog after going though dirty water (weed lines). There does not appear any real deposit build up in the block (thermostats, check valve, top of block screen.) I am at the point of pulling the block to see if there is a problem in the exhaust plate, but I was hoping someone might have a suggestion.<br /><br />thanks,<br />Joe 